Ioan Kosztin and Klaus Schulten.
Structure, function, and quantum dynamics of pigment-protein
complexes.
In Masoud Mohseni, Yasser Omar, Greg Engel, and Martin B. Plenio,
editors, Quantum Effects in Biology, pp. 123-143. Cambridge University
Press, 2014.
KOSZ2014
Pigment - protein complexes serve as sensors, light-driven ion pumps, as well as light
harvesting elements in many living cells. Their function, based on the interaction of
pigment electrons with the sun light, is grounded in quantum physics. The function is
greatly affected by geometrical constraints of the proteins that typically arrange pigments
in closely interacting groups exhibiting strong inter-pigment quantum coherence in the
form of excitonic coupling. The quantum mechanical properties of the pigment-protein
complexes arise despite the relatively high, namely physiological, temperatures found in
living cells. The pigment-protein complexes found in cells do not only avoid degradation
through thermal effects, but rather exploit thermal quantum behavior to improve their
functional characteristics. This is demonstrated in this chapter for the optical transitions
found in pigment-protein complexes as well as for electron transfer reactions initiated by
electronically excited pigments. After an introduction of pigment-protein complexes of
photosynthetic light harvesting complexes, the theory of thermally assisted optical
transitions and electron transfer is described and applied. The readers are introduced to a
fascinating chapter of physical biology, namely quantum behavior at elevated
temperatures. The resulting effects are often avoided in other fields of physics, where
quantum phenomena are studied preferably under conditions of low temperature, but
these effects are essential in quantum biology given the temperature preference of living
cells.
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